fsmonitor: read entirety of watchman output

Alex Vandiver · gitster · commit 2a387b17c5bc · 2017-10-04T18:58:53.000+09:00
In Perl, setting $/ sets the string that is used as the "record
separator," which sets the boundary that the `&lt;&gt;` construct reads to.
Setting `local $/ = 0666;` evaluates the octal, getting 438, and
stringifies it.  Thus, the later read from `&lt;CHLD_OUT&gt;` stops as soon
as it encounters the string "438" in the watchman output, yielding
invalid JSON; repositories containing filenames with SHA1 hashes are
able to trip this easily.

Set `$/` to undefined, thus slurping all output from watchman.  Also
close STDIN which is provided to watchman, to better guarantee that we
cannot deadlock with watchman while both attempting to read.

Signed-off-by: Alex Vandiver &lt;alexmv@dropbox.com&gt;
Signed-off-by: Junio C Hamano &lt;gitster@pobox.com&gt;
diff --git a/t/t7519/fsmonitor-watchman b/t/t7519/fsmonitor-watchman
@@ -50,9 +50,6 @@ launch_watchman();
 
 sub launch_watchman {
 
-	# Set input record separator
-	local $/ = 0666;
-
 	my $pid = open2(\*CHLD_OUT, \*CHLD_IN, 'watchman -j')
 	    or die "open2() failed: $!\n" .
 	    "Falling back to scanning...\n";
@@ -83,7 +80,8 @@ sub launch_watchman {
 	close $fh;
 
 	print CHLD_IN $query;
-	my $response = <CHLD_OUT>;
+	close CHLD_IN;
+	my $response = do {local $/; <CHLD_OUT>};
 
 	open ($fh, ">", ".git/watchman-response.json");
 	print $fh $response;
diff --git a/templates/hooks--fsmonitor-watchman.sample b/templates/hooks--fsmonitor-watchman.sample
@@ -49,9 +49,6 @@ launch_watchman();
 
 sub launch_watchman {
 
-	# Set input record separator
-	local $/ = 0666;
-
 	my $pid = open2(\*CHLD_OUT, \*CHLD_IN, 'watchman -j')
 	    or die "open2() failed: $!\n" .
 	    "Falling back to scanning...\n";
@@ -78,7 +75,8 @@ sub launch_watchman {
 	END
 
 	print CHLD_IN $query;
-	my $response = <CHLD_OUT>;
+	close CHLD_IN;
+	my $response = do {local $/; <CHLD_OUT>};
 
 	die "Watchman: command returned no output.\n" .
 	    "Falling back to scanning...\n" if $response eq "";
